Pardon this extended introduction to Jim Benford’s response to Nick Nielsen’s Friday essay, but it comes at a serendipitous time. Jim’s recent online work has reminded me that we in the interstellar community need to work to see that as many resources as possible are made available online. In the absence of specialized bibliographies, useful information can be hard to find in more general indices. And it’s always dismaying to read an intriguing abstract only to realize that the paper itself is behind a pricey firewall. Access to academic libraries certainly helps, but online databases still vary in what they make available, which is why I always check the home pages of the authors of a given paper to see if they have posted a copy of their work themselves. Scientists can do much to get the word out, as Jim’s new site attests.

You’ll find it at Over the weekend, after Nick had discussed METI (Messaging to Extraterrestrial Intelligence) on Friday, I resorted to Jim’s site to pull the Benfords’ key papers on cost-optimized interstellar beacons back up on screen. Preprints of these are available on the arXiv site, but how much more useful to have a single site with a researcher’s papers not just in preprint but in final form. Jim and brother Greg’s work on how beacons might be built, what their broadcasting strategies would likely be, and how we might go about finding them is moving SETI in interesting directions and it’s all here in one place.

So are references to Jim extensive work on microwave beaming to sailcraft, on fusion and pulsed power and plasma physics at large. Here we’re still limited to bibliographic entries because of publishers’ policies, but the bibliography is itself a valuable tool, and we can hope, as publishers gain more experience with networked resources, that open access to scientific work (particularly that funded by taxpayers!) will increasingly become the norm. Interstellar studies needs good bibliographers and researchers can help by cataloguing their own work.

But enough of this extended introduction to the response Jim sent to Nick. What to do about sending messages to other stars? For that matter, just how far are our own electromagnetic signals traveling? We have much to learn as the investigation continues.

by James Benford


I’m very pleased to see Nick Nielsen’s essay. Fits my attempts to widen the discussion of METI. METI is an issue that really should be debated further; as it is increasingly possible that someone will announce us. These are not easy questions; they are ultimately social questions, so should be widely discussed.

I would suggest another paper of mine which treats METI directly. It’s in the Special Issue of JBIS on the METI Debate that I am editing:

“Costs and Difficulties of large-scale METI, and the Need for International Debate on Potential Risks”, John Billingham and James Benford, in press, JBIS (2014).

A draft version is on my new website, at

A few comments:

1) Opponents of METI do not ‘maintain that the “leakage” of the ordinary (unintentional) EM radiation of a technological civilization cannot be detected at interstellar distances”. No, they say just that past signals are undetectable using our present and projected technology. Future leakage may well be larger – see the following point.

2) Several of the responses to my quantitative arguments showing that neither Earth-scale radio telescopes or even the Square Kilometer Array (SKA, that radio astronomers hope to build, but have yet to find the funding for) are able to detect leakage radiation or messages from our radio telescopes only at very limited range of at most a few light years. Their responses simply say that ETI will have far larger radio telescopes as big as Chicago or New Hampshire.

It’s not that easy. Such assumptions are not without implications. The proper scientific thing is to consider the implications of such assumptions. Larger-scale civilizations will leave larger footprints.

If we use Claudio Maccone’s statistical argument that results in the nearest ET civilization being roughly 1000 light years away, no message we can transmit from Earth within the limits of our technology would be detected unless the receiving civilization were substantially wealthier than us, by a factor of 1,000. The details: If we use the ability to build larger area radio telescopes as an indicator of the scale of civilization, that means the energies consumed, and so the wealth, should be larger by a similar amount.

Are there observable features of such civilizations? I think so, especially if they are nearby. If there were a civilization at Alpha Centauri with 1,000 times the energy consumption of earth, they would be able to do extraordinary things. They might modify their climate, beam power around their solar system, construct and launch starships, such as the ‘sailships’, beam-powered sails that Project Forward is conceptualizing. They would be observable.

So just imagining that ET is far more powerful than we are is not a simple escape clause from the arguments I made.

3) My work with John Billingham shows what METI would cost us: ~ 10 B$ for 1000 light year range. Countering METI would cost more than METI, but of same order. To suppress METI, radiate the same signal exactly 180° out of phase so that it cancels, suppressing the message.

4) “Energy and material limitations will cease to be relevant for all practical purposes.” That’s doubtful, as economic history shows. I remember when nuclear power was going to make electricity ‘free’. Didn’t happen. What does happen is prices for some things fall. For example Al, rare before 1800, now used for Coke cans.

5) Spectroscopy of exoplanet atmospheres could reveal markers of life like oxygen, but markers of civilization are very hard to see. Can anyone give an example of something detectable? CFCs aren’t, they’re too small.